1. Field of the Invention
In manufacturing velour-like textiles, the process of severing pile loops in pile forming machines is of considerable economical and ecological importance, inasmuch as the subsequent shearing of loops necessarily results in considerable loss of pile material. Such losses can be avoided by producing cut pile textiles.
2. Description of the Prior Art
In the past, a plurality of methods for manufacturing cut pile textiles have been developed. Regardless of the type of materials being used to make the product, however, only those methods which severed pile loops by two cutting edges, cooperating in a scissor-like manner, were successful under practical conditions.
Early proposals of this type of mechanism for manufacturing cut pile fabrics on loopwheel machines are described in DE-A-73 161, DE-A-77 975 and DE-A79 328 (corresponding to U.S. Pat. No. 2,579,621). A cutting element is associated with each pile element or sinker. The cutting element is mounted together with or separately from the pile element and is actuated relatively thereto for severing pile loops. The cutting edge of the cutting element is disposed at an angle, usually called an opening angle, with the cutting edge of the pile element, such that both edges are disposed in a V-like configuration prior to the cutting movement which brings them together like a pair of scissors.
This basic concept was subsequently transferred to manufacturing carpets in tufting machines, as described in U.S. Pat. No. 2,335,487, and to the manufacturing cut pile fabrics on circular knitting machines, for example, according to DE-A2-11 53 452 and DE-A2-15 85 051.
Particularly in the case of a laterally adjacent arrangement of pile elements and cutting elements, the cutting movement has been performed with an inadequate side pressure between the cutting edges. Therefore, it is easily possible for the cutting edges of the cutting and pile elements to be deflected by the unsevered pile loops encircling the pile elements. This may happen particularly if the pile loops are tightly enclosed around the pile elements and if the pile yarn is, furthermore, a material having high tenacity and/or abrasion resistance.
In order to obtain increased contact pressure between the cutting elements and the pile elements, and to permit the possibility of setting such contact pressure in accordance with the pile yarn material, the cutting elements on tufting machines were mounted separately from the pile elements and, starting out on the side of the active flank of the pile element, i.e. the flank comprising the cutting edge, were arranged to resiliently contact the latter at a relative inclination or pressurized contact angle.
Since the nibs of the cutting elements contact the pile elements as a result of the inclined arrangement of the cutting elements, a risk is created of obstructing contact between the cutting edges of the cutting elements and the cooperating cutting edges of the pile elements, and the flanks of the cutting elements are also arranged to be inclined with respect to the pile elements. Therefore, prior to the cutting movement, the cutting edges of pile elements and cutting elements have a corresponding overlapping configuration, referenced as a cutting angle, and the elements have only one point of contact. This point of contact shifts during the cutting movement from the lower ends of the cutting edges across their entire length to their upper ends and in the process deflects the overlapping part of the cutting elements from the pile elements. The gap created thereby is to prevent pinching of severed pile loops and deflection of the cutting edges being separated.
Therefore, this cutting angle between the two elements is of particular importance. The cutting angle must be dimensioned to sufficiently separate the elements after the cutting point and to also avoid pinching of pile loops. In tufting machines, the cutting movement is performed by a relative movement of the mounting bar of the cutting elements in parallel with the flanks of the pile elements. A constant contact pressure between the elements is ensured exclusively by an adequate cutting angle in combination with a shallow angle under which the cutting element is pressed against the pile element during the cutting motion.
These same conditions, in combination with a restricted opening between the respective cutting edges, ensured that the flanks of the cutting elements projecting between the pile elements cannot contact the pile elements with their front ends and cause a reduced contact pressure between the cutting edges or even their separation, respectively. As an increased cutting angle will, however, also intensify wear of the cutting edges, and must therefore be avoided, the requirements to the dimensions of cutting, opening and pressurized contact angles are in direct contradiction.
Due to the contact angle of the cutting element to the pile element, the required contact pressure for severing the pile loops is obtained, whereby the cutting elements are flexibly bent. Therefore, the pressurized contact angle is smaller in the area of the cutting edges than in the mounting area as a function of the material thickness.
The thickness of the cutting elements is determined by the gauge and by the thickness of the pile elements. The pile elements must be of a sufficient size that the cutting angle cannot be reduced or neutralized by a deflection of the pile elements as a result of pressurized contact with the cutting elements. The maximum thickness of the cutting elements is, therefore, determined by the gauge and the thickness of the pile elements under consideration of the pressurized contact angle and the cutting angle. To obtain cutting elements having sufficient strength on finer gauge tufting machines, the inactive flanks of the pile elements opposite the cutting edges are partially bevelled to obtain the required space in between the pile elements. Adequate strength of the cutting elements is necessary to avoid torsional forces in the transverse axis of the cutting elements whereby also the cutting angle of the cutting edges may be reduced or neutralized, respectively, and the cutting elements would contact the pile elements with their front ends.
Under the above described conditions it is obvious that owing to adequate contact and cutting angles a reduction of the space in between the pile elements is limited and tufting machines with a gauge of less than 1/10 in. are regarded as a fine gauge machine.
The above described conditions for severing pile loops were applied to a circular knitting machine for manufacturing cut pile fabric according to the proposal of EP-A2-0 082 538 (corresponding to U.S. Pat. No. 4,592,212) keeping in mind consideration of the requirements for a correct fabric construction. In order to permit sufficient dimensions of the pile and cutting elements in view of the reduced space between pile and cutting elements required for the respective usual gauges of 18 or 20 needles per inch, it was necessary to reduce the angles required for the severing operation, especially the pressure contact angle. This was realized by a reduced distance between the cutting edges and the mounting of the cutting elements in the sinker ring.
Owing to the fact that the cutting elements in circular knitting machines are moved in their fixed mounting during the cutting movement, an increased contact pressure resulted even under a smaller pressure contact angle. This increased the possibility of the pile element being deflected in a lateral direction, or the cutting edge of the cutting element being twisted, both of which can cause the above described negative consequences in severing pile loops.
As can be gathered from the foregoing description of the presently applied methods for severing pile loops in pile forming textile machines, satisfactory severing of the pile loops along with a fairly suitable service life for the cutting edges will result only from an extremely precise harmonization of the dimensions of pile and cutting elements and of the contact, opening and cutting angles of these parts. A particular disadvantage resides in the limitation of the range of gauges.